I had to read it 3 times before it made sense,you mean what can the operator of a pat testing machine do. well you don't have to be a qualified spark to repair machinery,in the same vein that you do not have to hold a PAT testing certificate to carry out PAT testing.The whole thing in law revolves around the question of competency,A person may be a qualified spark but that does not mean he is competent to work on certain equipment,in the same way that someone may hold a PAT certificate and not be fully competent at testing,this is something we see all to often these days.If you understand the equipment that you are working on then you may repair it,however if it went wrong would you be able to prove beyond doubt in a court of law that you were COMPETENT to do what you did? That is the sticky bit.